The code P0343: “Camshaft Position Sensor ‘A’ Circuit High Input” indicates an issue with the electrical signal from the camshaft position sensor to the engine control module (ECM). This fault can lead to engine performance problems, such as difficulty starting, rough idling, and possible stalling.
P0343 quick overview
| Meaning | P0343: Camshaft Position Sensor ‘A’ Circuit High Input |
| Is it serious? | Yes, it can affect engine performance and reliability. |
| Possible causes | – Faulty camshaft position sensor – Timing belt or chain issues – Wiring or connector problems related to the camshaft position sensor – Blocked or malfunctioning catalytic converter – Engine control module (ECM) issues |
| How to diagnose? | Inspect Camshaft Sensor: Check for damage or disconnection. Check Timing Components: Verify timing belt or chain alignment. Evaluate Wiring and Connectors: Look for damage or loose connections in the sensor circuit. Measure Engine Vacuum: Assess vacuum levels for indications of timing issues. Test Fuel System: Check fuel pressure and related components. Inspect Exhaust System: Evaluate for blockages or issues with the catalytic converter. Assess ECM: Consider the health of the engine control module. |
P0343 Meaning
In simple terms, the P0343 code means there’s a problem with the signal coming from a sensor that tells your engine when to fire its cylinders. This sensor called the camshaft position sensor, plays a crucial role in your car’s ability to start and run smoothly. If this sensor isn’t working right, or if the signal it sends is too strong (high), your engine might have trouble starting, run unevenly, or even stall. This issue could be due to the sensor itself, its wiring, or even a problem with the engine’s timing components. It’s important to get this checked out to ensure your car runs reliably.
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How to fix P0343 – learn from mechanics
I looked into P0343 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: GMC
Vehicle Information
- 2002 GMC Sierra 2500 6.0L
Issue + Repair History
- MIL light on
- Found hard code P0342 (cam sensor signal low), replaced with updated cam sensor
- New issue with code P0343 (cam sensor signal high) after sensor replacement
Other OBD2 Codes + Test Results
- P0342 – Cam Sensor Signal Low
- P0343 – Cam Sensor Signal High
Suggested Fixes
- Ensure updated cam sensor part number as per TSB
- Perform crank relearn procedure
- Check if the distributor has been replaced, removed, or moved; realign if necessary
- Consider the possibility of a faulty replacement sensor
Final Fix
- Used a .025 gasket as a spacer for the cam sensor to resolve the issue
- No more codes after starting the truck multiple times
- Issue with hard starting also resolved
Case #2: Chevrolet
Vehicle Information
- 2001 Chevrolet Suburban 2500 8.1L
Issue + Repair History
- MIL light on after new Camshaft Position (CMP) sensor installation
- Code P0343 appeared a couple of days after replacement
- Scoped sensor and wiggled harness, with no change observed in CMP PID on scan tool
- Failure indicated at idle speed, no load, in park/neutral
- MIL lamp turned off after starting the vehicle again two days later
Other OBD2 Codes + Test Results
- P0342 – CMP Low Voltage
- P0343 – CMP High Voltage
- 12V signal at CMP, low reference circuit, and signal with labscope all normal
Suggested Fixes
- Check synchronization of CMP signal with scanner
- Scope CMP signal at computer or use scanner to check signal on scan graph
- Inspect the Vehicle Control Module (VCM) for corrosion
Final Fix
- Found corrosion inside the VCM
- Identified and resolved by replacing the VCM
Case #3: Volkswagen
Vehicle Information
- 2001 Volkswagen Beetle GLS 2.0L
Issue + Repair History
- MIL light initially not on, but code 16727/P0343 set in history for cam sensor
- Tested cam sensor, signal consistently good
- No code reset after clearing and test driving
- Lab scope showed 12V out of the signal wire with the key out of the ignition intermittently
- Engine misfire at idle noted, but no misfires in blocks 14 & 15
Other OBD2 Codes + Test Results
- 16727- P0343 Cam Sensor Signal High
Suggested Fixes
- Check distributor timing and timing belt
- Replace the cam sensor, especially if using non-genuine parts
- Verify cam timing
- Ensure adequate oil pressure and check camshaft adjustment motor
Final Fix
- Replaced cam sensor after confirming cam timing was correct
- No recurrence of the code after a prolonged period
Case #4: Hyundai
Vehicle Information
- 1999 Hyundai Elantra GL 2.0L
Issue + Repair History
- Persistent code P0343, causing long cranking times before starting
- Replaced cam sensor, despite good square wave, but issue persisted
- Checked crank sensor; waveform varied significantly
- Replaced with new OEM crank sensor; waveform similar to the old one
- Timing was off by one tooth
Other OBD2 Codes + Test Results
- P0343 – Camshaft Position Sensor A High
- Crank sensor waveform varied from 14V to 26V (AC)
Suggested Fixes
- Check belt timing for skipped teeth or missing teeth
- Consider the possibility of a camshaft or crankshaft sensor problem
- Evaluate camshaft and crankshaft synchronization
- Check wiring to PCM and PCM ground
- Review vehicle’s grounding and electrical resistance
Final Fix
- Adjusted timing which was off by one tooth
- Left crank sensor as is, given that the check engine light did not return
- No specific resistance range for the crank sensor could be confirmed
Case #5: Kia
Vehicle Information
- 1999 Kia Sportage 2.0L
Issue + Repair History
- Extended cranking, hesitation, lack of power on startup
- Black spark plugs, low vacuum (8 lbs)
- Cam sensor code P0343
- No change after dropping the converter and checking back pressure
Other OBD2 Codes + Test Results
- P0343 – Cam Position Sensor Circuit High Input
- Manifold Vacuum Readings at Idle: 8 in.
- Fuel Pressure: 43 lbs
Suggested Fixes
- Check basics like cam timing or restricted exhaust
- Consider if catalytic converter is clogged
- Check the pressure regulator for leaks
- Inspect the timing belt for alignment issues
Final Fix
- Identified timing issue due to worn crank gear keyway and crank
- Ordered new parts and welded the crank to fit the keyway
- Resolved timing issue, improving engine performance
How to diagnose P0343
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Common Advice for Solving Code P0343 | Diagnostic Step Description |
|---|---|
| Check Cam and Crank Timing | Verify the alignment of cam and crankshaft timing, including timing belts or chains. |
| Inspect Cam and Crank Sensors | Examine the camshaft and crankshaft sensors for damage, proper connection, and signal integrity. |
| Evaluate Engine Vacuum | Measure the engine’s vacuum to identify potential timing or air intake issues. |
| Assess Fuel System | Check the fuel pressure and fuel system components for proper operation. |
| Investigate Exhaust System | Look for any blockages or restrictions in the exhaust system, including the catalytic converter. |
| Consider ECM/PCM Health | Evaluate the engine control module or powertrain control module for any signs of malfunction or corrosion. |
Car Diagnostics Training
- Car Electrical basics
- OBD-II scanner basics
- How to use an OBD reader
- Introduction to a Bi-directional Scan tool
- OBD scanner buyer’s guide + discounts
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko